The present invention relates generally to the field of weather radar.
Pilots use weather radar systems to detect and avoid hazardous weather. The radar return signals are processed to provide graphical images to a radar display. Weather radar systems generally include an antenna, a receiver/transmitter circuit, a processor and a display. The processor is coupled between the display and the receiver/transmitter circuit. The receiver/transmitter circuit is coupled between the processor and the antenna.
The processor provides transmit signals through the receiver/transmitter circuit to the antenna to transmit radar beams. The processor receives radar return signals derived from radar returns received by the antenna. The radar return signals are provided to the processor via the receiver/transmitter circuit.
Airborne weather radar systems are known to display vertical views of weather, where the axes are range and altitude, where the weather radar may produce a vertical weather display from multiple horizontal sweeps or a dedicated vertical sweep.
Multiple multi-scan weather radar algorithms require knowledge of the vertical location of the radar reflections. An important issue in estimating the vertical location is that the 3 dB beamwidth of an airborne weather radar antenna is very large. For example, for a typical 18 inch antenna used in airborne weather radar systems, the beamwidth is about 5 degrees. At 100 nautical miles (Nmi) in range, the width of the beam is 55 kilofeet (kft).
The broad beam resolution may result in a storm top altitude estimation error from vertical sweeps, where the altitude estimation error increases with range. The altitude estimation error may affect the accuracy of the vertical weather display, and the ability of the weather detection system to identify and detect growing weather cells.
FIG. 1 is a graph illustrating the amount of error in altitude expected from an 18 inch antenna with a 3 dB beamwidth as a function of range. Each line represents a weather cell with varying characteristics. Note that at a range of 100 Nmi the storm top error may range from 20 kft to 30 kft depending on the weather type.
One way to counteract the effects of large beamwidth is with beam deconvolution. Beam deconvolution is a method in which the shape of the main beam in essentially sharpened using signal processing methods. Methods such as inverse filtering or Wiener filtering, for example, may be used to deconvolve the beam. These processes, however, are computationally expensive and require large amounts of data to work well.